140 The Lymphocyte and Lymphocytic Tissue 



the lymphocytes returned to normal in about 30 days after irradiation. 



After a single total body exposure of rabbits, the lymphocyte count re- 

 turned to normal in 2 days after 25 r and in 50 days or more after 400 r of 

 total body irradiation. 1 ' 1 In contrast it took only 9 days for the granulocyte 

 count to return to normal after 500 r. The lymphocyte is the first cell to 

 degenerate after total body irradiation and the last to return to normal. 

 The animals had no compensatory absolute lymphocytosis after acute total 

 body irradiation." 



Rabbits irradiated with 400 r show recovery of the histologic structure 

 of lymphoid tissue in 5 days and the recovery of the number of blood 

 lymphocytes in about 50 days. Recovery is not as rapid in blood lymphocytes 

 as in lymphoid tissue. 8 



The slowness of the return of the normal lymphocyte count is especially 

 prominent in man. After total body irradiation with only 60 r, the lympho- 

 cyte count did not return to normal even after 5 months in two of four 

 individuals. 40 Two individuals who were accidentally irradiated continued 

 to have lymphopenia 1 to 2 years after the accident. 10 Two years after a high 

 dosage of total body exposure from the Hiroshima atom bomb, survivors 

 had a slightly lower lymphocyte count than a control population. r,c After 

 therapeutic irradiation with x-rays or radium, the recovery period was 1 to 

 19 weeks with an average of 5 weeks in one study-"' and at least from 4 to 

 6 weeks in another. 15 



Species Effect 



According to Jacobson and associates, 22 man shows the same degree of 

 radiosensitivity of lymphocytes as the guinea pig and the dog. The qualita- 

 tive changes in the blood are the same in man and lower animals. 9 The chief 

 difference in the hematologic response of man and animals is in temporal 

 relations. 37 After total body irradiation with about 400 r, the lymphopenia 

 developed within 2 days in the rabbit and within 5 days in man. The abor- 

 tive rise of blood lymphocytes was observed in from 4 to 1 1 days in the 

 rabbit and at from 17 to L M) days in one man. Lymphoid tissue showed 

 abortive recovery in 10 to 36 hours after 1000 r in mice and probably in 3 

 days to several weeks in man after lethal irradiation. Recovery of the normal 

 lymphocyte count occurred in about 2 months in rabbits after a large dose 

 of x-rays, but it took 2 years or more for a man to recover. An irradiated 

 man takes a longer time to reach minimal leukocytic levels and to recover 

 normal levels than irradiated laboratory animals. 



According to the in vitro findings that I have described, the lymphocytes 

 of men and lower animals have approximately similar radiosensitivities. 



